Heatpump question - split system vs single

Users who are viewing this thread

yds

New Member
Messages
10
Reaction score
0
Points
0
Location
Toronto, Ontario
Hi. I'm in the process of building a new third floor on top of my two storey semi-detached downtown toronto home. It will contain a master bedroom, ensuire bathroom, reading area and small deck. Total floorspace of just under 500 sqft. The plans call for a supplemental HVAC system for this floor. I had originally figured a split system ductless would be the right choice. I've attached the floorplan below.

I had a discussion with my contractor yesterday. The HVAC guy that he is dealing with has suggested that I don't need a split system, just a single outlet that will supply the heat and cooling to the entire floor. The contractor is saying that if the outlet is located over the sliding doors to the deck it will sufficient to get heat and cooling to all rooms, with a supplemental electric register for when it gets really cold occasionally. I'm concerned however that the bedroom would not get sufficient heat/cool, especially when we have the door to the hallway closed (we would typically leave it open during the day, but close it at night). Note that the floor in the ensuite bathroom will have radiant heat, so it would probably be ok heatwise in any case.

My thought was that it would be a split system with one outlet over the sliding door, and one outlet in our bedroom. Still with an electric register in both rooms for when it gets really cold.

Any professional advice out there?

3rdfloor-1.jpg
 

Lightwave

New Member
Messages
98
Reaction score
0
Points
0
Location
Vancouver, BC
1.
Can you define your terms more clearly?
What do you mean by 'split system?' A ductless heat pump with two indoor units?
What does your GC's HVAC guy mean by a 'single outlet?' A ductless heat pump with one indoor unit or something else entirely?

2.
A single head ductless unit will not handle three rooms under any circumstances. You need a register or ductless unit in every room. You can use a single specialized ducted minisplit to heat/cool two rooms--you could handle the bdrm and ensuite this way, but you'll need another unit for the reading room.

You can drive two indoor minisplits from a single outdoor compressor.

Heat pumps produce less heat as outdoor temperatures decline. They must sized to meet your heating requirements at the coldest temperature you expect the heat pump to handle without help from another heater. This switchover temperature is known as balance point. Sizing is a matter of doing a Manual J load calculation at balance point and then using heat pump manufacturer's published heat output ratings at the intended balance point to determine the correct unit size. Oversizing a minisplit for heating will not--in contrast to oversizing a full-sized heat pump--harm cooling performance.

No minisplit will produce useful heat at outdoor temperatures below -4f/-20c. Many will shut down entirely at -14f/-10c. Given Toronto's climate, you must have a supplemental heat source capable of carrying the entire heating load for the addition in cold weather. Use Manual J to size the supplemental heat source.

If you have natural gas, a gas fireplace (for the bdrm) and wall furnace (for the reading room) will work nicely for supplemental heat. If you don't have gas, then look at baseboard heaters, underfloor radiant, or radiant panels.

For the heat pump, look closely at Daikin's multi-head MXS system. These have very good cold weather performance and support both ductless and ducted indoor units. Daikin 4MXS32GVJU is probably adequate for your needs but you need a load calc for a definitive answer.


Sizing minisplits heat pumps for this application is a niche job that few HVAC contractors are able to handle. If your GC's HVAC guy doesn't understand all of the above like the back of his hand, find another HVAC contractor with a strong background working with minisplits.
 

Gator37

Retired prof. engr.
Messages
108
Reaction score
0
Points
0
Location
Alabama
You will not be happy with one outlet in either one of the rooms. If you can get an outlet in each room that would be good. You also need an exhaust in the toilet and undercut the door (1/2") to allow makeup air to the exhaust fan.
It does not matter if you use a conventional split or a package system as long as it gets the job done. A conventional split would need a place for the inside unit plus ducting.
If you are thinking about a split ductless system I would recommend a Mitsubitisi (or similar system) with two mini AHUs assuming you have room above the ceiling. This type of system also has more control advantage but is typically more expensive. You will also need a place for the condenser unit outside.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks